FIGS. 15 and 16 (see JP 2005-174901A) show, for example, a conventional electrical connector 101 for electrically connecting an IC package 130 to a circuit board 140. In FIGS. 15 and 16, the conventional electrical connector 101 comprises an insulating housing 110 and a plurality of contacts 120 secured to the housing 110. The housing 110 comprises a substantially rectangular plate-form base 111 that is mounted on the circuit board 140 and side walls 112 consisting of four sides rising from the edges of the base 111. A rectangular opening 117 is formed in a central portion of the base 111, and a plurality of contact accommodating cavities 118 are arranged in the form of a matrix so as to surround the opening 117. Furthermore, the space surrounded by the side walls 112 consisting of the four sides and the base 111 forms a package accommodating space 113 that accommodates the IC package 130. Moreover, elastic arms 114 are provided on two of the adjacent side walls 112 out of the four side walls 112.
As is shown in FIGS. 17A, 17B, 17C, 17D, and 17E, each contact 120 comprises a base plate 121 that is formed in a substantially rectangular plate form, a first elastic contact arm 122 that extends upward from the base plate 121, and a second elastic contact arm 123 that extends downward from the base plate 121; each of the contacts 120 is formed by stamping and forming a metal plate. Here, the base plate 121 is designed such that both left and right side edges thereof are press-fitted into one of the contact accommodating cavities 118 in the housing 110.
The first elastic contact arm 122 is formed in a cantilever shape comprising a base 122a that extends from a central portion in a direction of width of an upper edge of the base plate 121, an arm 122b that extends forward at an inclination toward the top from an upper end of the base 122a with the width thereof being gradually reduced toward a tip end 122d, a contact member 122c that is formed by bending at the tip end of the arm 122b, and the tip end 122d that extends forward at an inclination toward the bottom from the contact member 122c. A pair of cutouts 124 for allowing the first elastic contact arm 122 to flex easily in a vertical direction are formed in either side of the base 122a in the direction of width. Furthermore, in a state in which the base plate 121 is press-fitted into the contact accommodating cavity 118 in the housing 110, the arm 122b, the contact member 122c, and the tip end 122d of the first elastic contact arm 122 are designed to protrude upward from the upper surface of the base 111 of the housing 110. Moreover, when the IC package 130 is accommodated in the package accommodating space 113, a conductive pad (not shown in the figures) provided on an undersurface of the IC package 130 contacts the contact member 122c from above.
In addition, the second elastic contact arm 123 is formed in a shape symmetrical to the first elastic contact arm 122, and is formed in a cantilever shape comprising a base 123a that extends from the central portion in the direction of width of a lower edge of the base plate 121, an arm 123b that extends forward at an inclination toward the bottom from the lower end of the base 123a with the width thereof being gradually reduced toward a tip end 123d, a contact member 123c that is formed by bending at a tip end of the arm 123b, and the tip end 123d that extends forward at an inclination toward the top from the contact member 123c. A pair of cutouts 124 for allowing the second elastic contact arm 123 to flex easily in the vertical direction are formed in either side of the base 123a in the direction of width. Furthermore, in a state in which the base plate 121 is press-fitted into the contact accommodating cavity 118 in the housing 110, the arm 123b, the contact member 123c, and the tip end 123d of the second elastic contact arm 123 are designed to protrude downward from the undersurface of the base 111 of the housing 110. Moreover, when the conventional electrical connector 101 is mounted on the circuit board 140, a conductive pad (not shown in the figures) provided on an upper surface of the circuit board 140 contacts the contact member 123c from below.
Here, when the IC package 130 is accommodated in the package accommodating space 113 from above, sides of the IC package 130 press the elastic arms 114 provided on the side walls 112, and cause the elastic arms 114 to be elastically deformed and move toward the side walls 112, so that the IC package 130 is prevented from slipping out of the package accommodating space 113 by the elastic force of the elastic arms 114. In this case, furthermore, the conductive pads (not shown in the figures) provided on the IC package 130 contact the contact members 122c, and the conductive pads (not shown in the figures) provided on the circuit board 140 contact the contact members 123c; moreover, the conductive pads (not shown in the figures) of the IC package 130 press the contact members 122c, and the conductive pads of the circuit board 140 press the contact members 123c, so that the first elastic contact arms 122 and the second elastic contact arms 123 of the contacts 120 flex, and respectively undergo elastic displacement in the vertical direction so as to approach each other, thus realizing the secure electrical connection between the IC package 130 and the circuit board 140. Furthermore, when the first elastic contact arms 122 and the second elastic contact arms 123 of the contacts 120 flex, and respectively undergo elastic displacement in the vertical direction so as to approach each other, the contact pressure against the contact members 122c and the contact pressure against the contact members 123c are respectively imparted by the elastic forces of the first elastic contact arms 122 and the second elastic contact arms 123, thus obtaining the contact reliability of the contact members 122c and 123c. 
Moreover, when the conductive pads (not shown in the figures) provided on the IC package 130 contact and press the contact members 122c, and the conductive pads (not shown in the figures) provided on the circuit board 140 contact and press the contact members 123c, the respective first elastic contact arms 122 and the second elastic contact arms 123 are elastically displaced in the horizontal direction as well, so that the contact members 122c and the contact members 123c horizontally move toward the adjacent contacts 120. In this case, between two of the contact accommodating cavities 118, a first projection 115 is disposed on the upper side, and a second projection 116 is disposed on the lower side; accordingly, when the contact members 122c and the contact members 123c reach certain positions, the free ends of the first elastic contact arms 122 contact the side surfaces of the first projections 115, and the free ends of the second elastic contact arms 123 contact the side surfaces of the second projections 116, so that it is possible to prevent the plastic deformation of the first elastic contact arms 122 and the second elastic contact arms 123 caused by the application of an excessive force.
However, the following problems have been encountered in the conventional electrical connector 101. Specifically, there are cases in which the IC package 130 or the circuit board 140 is warped or deformed for some reason. In such cases, when the conductive pads (not shown in the figures) provided on the IC package 130 contact and press the contact members 122c, and the conductive pads (not shown in the figures) provided on the circuit board 140 contact and press the contact members 123c, it is not possible to obtain a desired amount of flexing of the first elastic contact arms 122 and the second elastic contact arms 123 of the contacts 120 in the vertical direction. As a result, a desired elastic force of the first elastic contact arms 122 and the second elastic contact arms 123 cannot be obtained, which makes it impossible to give the appropriate contact pressure against the contact members 122c and the appropriate contact pressure against the contact members 123c, so that the contact reliability of the contact members 122c and 123c may be insufficient.